A method honeycomb carrier for carrying a catalyst for cleaning automobile exhaust gas comprises a core part having a honeycomb cross section obtained by stacking flat steel plates and corrugated steel plates and winding round the stacked plates, and a metallic outer cylinder for containing the core part.
Since a high-temperature exhaust gas of the automobile recirculates in the metal honeycomb carrier, it is necessary that the outer diameter of the core part and the inner diameter of the outer cylinder are nearly equal to each other so that a clearance between both is as small as possible. For this purpose, various methods are used in inserting the core part into the outer cylinder. For example, Japanese Patent Publication 57-55886 discloses a method in which the core part is pressed into the outer cylinder, the diameter of the outer cylinder is reduced by a contracting tool capable of press-fitting the outer cylinder, and the core part and the outer cylinder are welded or soldered to an extent of press-fitting to link one another.
However, with this method, since the core part is difficult to adapt to the outer cylinder, a space tends to be left between the core part an the outer cylinder.
On the other hand, to clean an exhaust gas emitted from an internal combustion engine of automobiles, motorcycles, and the like, a core part comprising a honeycomb structure carrying a catalyst is pressed into an outer cylinder to form a metal honeycomb carrier, which is mounted in a gas cleaning apparatus, and the exhaust gas is passed through the carrier to clean the gas. However, a gas pipe for mounting the honeycomb carrier in the exhaust gas cleaning apparatus is not always circular, but often have elliptical or other specific shapes, and the cross section of the metal honeycomb carrier must be in line with the cross sectional shape of the gas pipe mounting the honeycomb carrier.
For this purpose, there has heretofore been known a method for producing a non-circular metal honeycomb carrier, in which after a circular honeycomb structure is pressed into an outer cylinder, a die is used to press the carrier to an oval or elliptical cross section (Japanese Patent Publication 57-55886).
However, this method has problems in that a deformation occurs in the cell shape between the longer diameter side and the shorter diameter side, and the joining strength is reduced or the cell density is varied, affecting the gas flow distribution.
As another method, a center part having a similar shape to a non-circular outer cylinder and having smaller cross sectional dimensions than the outer cylinder by predetermined values is formed, a flat plate and a corrugated plate are wound around the center part to form a core body, and the core body is pressed into the non-circular outer cylinder (Japanese Patent Laid-open Publication 3-196844).
However, this method has disadvantages in that since the center part is first fabricated, and the corrugated plate and the flat plate are wound round using the center part as a winding shaft into a honeycomb form, the production takes a long time and the productivity is low.
The inventors have conducted intensive studies to improve these problems so that the core part is easily engaged with the outer cylinder to link them securely, achieving the present invention. A primary object of the present invention is to provide a method for producing a metal honeycomb carrier having a good workability. A further object of the present invention is to provide a method for producing a metal honeycomb carrier in which a flat plate and a corrugated plate regularly contact with each other to form a type of ceil structure, without deforming the honeycomb structure.